planner: fix idxMergePartPlans forget to deal with RootTaskConds (#58507)

[ti-chi-bot]

This is an automated cherry-pick of #58507

What problem does this PR solve?

Issue Number: close #58476

Problem Summary:

What changed and how does it work?

fix idxMergePartPlans forget to deal with RootTaskConds

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

fix idxMergePartPlans forget to deal with RootTaskConds

修复在处理 idxMergePartPlans 时忘记处理 RootTaskConds 的问题

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please ask for approval from hawkingrei, ensuring that each of them provides their approval before proceeding. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• pkg/planner/OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (release-8.5@9a5b05a). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.5     #58520   +/-   ##
================================================
  Coverage               ?   56.9156%           
================================================
  Files                  ?       1770           
  Lines                  ?     626930           
  Branches               ?          0           
================================================
  Hits                   ?     356821           
  Misses                 ?     245932           
  Partials               ?      24177           

Flag	Coverage Δ
integration	36.8066% <100.0000%> (?)
unit	72.6159% <100.0000%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	52.8711% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	52.2793% <0.0000%> (?)